1589 · Beylerbeyi Incident (Revolt) — Mehmed Pasha, governor of Rumelia, and the chief treasurer Mahmud Efendi, whose heads the troops demanded, were killed; the grand vizier, …
1918 · Van (City) — Van was liberated on 2 April 1918; the new city was built 7 km from the old one.
6 April
1326 · Bursa (City) — Starving after the long blockade, the city surrendered to the Ottomans on 6 April 1326; Orhan Bey made Bursa his capital.
13 April
1909 · 31 March Incident (Revolt) — The Army of Action from Salonica took Istanbul (24 April); parliament deposed Abdülhamid II and enthroned Mehmed V Reşad (27 April 1909)
14 April
1566 · Chios (City) — Piyale Pasha's fleet took the island from the Genoese; the Genoese rulers were sent to Istanbul on 14 April 1566.
1919 · Antalya (City) — Citing the Armistice of Mudros, the Italians occupied the city on 29 April 1919.
Dates are given as in the sources; dates before 1582 are mostly Julian. Event dates come from Wikipedia infoboxes, city events from the city articles of the TDV Encyclopedia of Islam.